FWIW, several threads on the forum at TheSamba mention that you should
disconnect and then reconnect the O2 sensor with the ignition off to reset
the ECU.

I found a note in the VW Pro Training manual (
http://members.verizon.net/blumax/protrainingdigifantvanagon.htm ) on
Digifant I that says:

"NOTE: The oxygen sensor must be disconnected with the ignition off to
cancel the Digifant E.C.U. memory."

That quote is from the section called Oxygen Sensor - Checking, page 24.
They have you shut off the engine, disconnect the O2 sensor, start engine,
and then hold the O2 sensor wire to ground to watch the CO content rise. I
think the point of the NOTE quoted above is to tell us that you can't just
disconnect the sensor while the engine is running or the memory will not be
cleared.

I know a little bit about electronics, and I don't see how the memory would
change if you just disconnect and reconnect while there is no power applied
to the ECU. My guess is that the computer gets reset anytime you start the
engine with the O2 sensor disconnected.

Mike Frost